The present invention relates to an imaging device for printing characters or drawing figures on the surface of a recording paper being fed, and discharging the same.
A recording (image information) system for an imaging device such as a copying machine, printer, facsimile and the like is provided with a recording head movable in the width direction of a recording paper, or a recording head having recording elements disposed over the entire width direction of the recording paper. In this system, an image is formed while moving the recording paper in a direction perpendicular to which the recording head is moved or a direction perpendicular to the direction in which the elements are disposed. That is, in this system, a main scanning is carried out by the recording head and a auxiliary-scanning is carried out by the movement of the recording paper.
In the imaging device in which the auxiliary-scanning is carried out by the movement of the recording paper as described above, there is provided a holding member (clamper) capable of holding the extreme end of a recording paper. The clamper can be moved in the direction in which the recording paper is scanned and thus the recording paper is moved by moving the clamper which holds recording paper. This arrangement is often applied to a color imaging device which must carry out an image formation on the same recording paper a plurality of times because the movement of the recording paper can be precisely controlled by this arrangement.
Nevertheless, in the above arrangement for holding the extreme end of the recording paper by the clamper, a problem arises in that a paper discharge means must be provided in addition to the clamper. Further, the recording paper on which an image has been formed must be released from the clamper, and discharged by the paper discharge means, and thus the structure of the imaging device is made complex.
Further, to form an image with a pinpoint accuracy, the clamper must accurately hold the extreme end of the recording paper at the predetermined position thereof. For this purpose, a recording paper feed means must feed the recording paper while ensuring the extreme end thereof is parallel with the clamper. Thus, the feed of the recording paper from a recording paper accommodation unit to the clamper must be managed with a pinpoint accuracy, and the recording paper being fed must be stopped at a position having a proper positional relationship with the clamper at all times. However, it is difficult to feed all the recording papers to the pressed together contact portion of rollers in the state the recording papers (their attitudes) are in parallel with the pair of rollers, because respective recording papers have a different rigidity specific to them and may be sometimes curled. To cope with this problem, the structure of the imaging device is made more complex.
Further, in the arrangement wherein the recording paper is scanned/moved by being held by the clamper, since the clamper holds and pulls the extreme end of the recording paper to scan the recording paper for the formation of an image, a force is applied to the recording paper and relatively pulls the recording paper backward. When an image is formed on the same recording paper a plurality of times as in the formation of a color image, the clamper must be moved in a direction opposite to that of scanning operation to return the recording paper to a scanning start position. At this time, the recording paper is pulled backward when the rear end (the end opposite to the end held by the clamper) of the recording paper is pulled to feed the same in the reverse direction. Therefor, the position of the recording paper held by the clamper is dislocated by the force applied to the recording paper for pulling the same. As a result, there is a possibility that an image may be badly formed.
Further, in the arrangement wherein an image is formed by relatively moving the recording paper with respect to the recording head, the recording paper becomes charged with an electrostatic potential caused by the friction between the recording paper and the recording head. In this case, there is a possibility that the recording paper on which an image has been formed may be electrostatically attracted to a paper discharge path and cannot be discharged well or an electrostatic charge may be discharged from the recording paper discharged from the discharge path when a user touches the paper.
The aforesaid clamper is moved by an endless drive belt rotatably stretched about pulleys and relatively immovably fixed to the clamper at a predetermined position of the belt, serving as a rotating track in parallel with the scanning/movement direction of the clamper. In this case, the drive belt is usually composed of a timing belt which can be moved with a pinpoint accuracy without slipping. Nevertheless, fixing the clamper to the drive belt stretched about the pulleys is difficult and time consuming. Further, the dismounting and mounting of the clamper, necessary for maintenance, is also time consuming. Note, the arrangement for moving the moving member by the endless drive belt rotatably stretched about the pulleys is applied not only to the imaging device but also to an image reading device referred to as an image scanner to read an image by moving a reading head.
The aforesaid imaging device forms an image on a recording paper cut to a predetermined size. In this imaging device, a plurality of recording papers are accumulated and accommodated in a recording paper cassette and introduced into the device by an introduction means such as paper feed rollers, or the like, provided with a paper feed unit to which the recording paper cassette can be detachably mounted and fed to the position of the clamper along a predetermined path. Incidentally, in a color imaging device for forming a color image by carrying out an image formation on the same recording paper a plurality of times by using different colors, on the completion of an image formation by a color, the recording paper must be returned to an image formation start position for the repetition of the image formation using different colors.
The length of a recording paper feed path is inevitably increased to prevent the disadvantage that the rear end of the recording paper arriving at the paper feed unit interferes with the paper introduction means such as the paper feed rollers or the like when the recording paper is returned to the image formation start position. If, however, the length of the paper feed path is increased, a problem arises in that a paper feed drive system is made complex, a possibility of a paper jam is increased, and the size of the imaging device as a whole is also increased.
The recording head of the imaging device is disposed in confrontation with a platen roller. The platen roller has a surface composed of a material with a predetermined elasticity (such as rubber or the like); so that the platen roller is pressed against the recording head with a pressing force that is maintained as uniformly as possible. The recording paper, held and moved (sub-scanned) by the clamper, is pressed against and caused to intimately contact with the recording head, by the platen roller. When the recording paper is fed by being held by the clamper, the recording paper must be fed between the recording head and the platen roller. For this purpose, the recording head is arranged to be spaced apart from the platen roller. It is logical to arrange the imaging device in such a manner that the platen roller and recording head are disposed on one side of the imaging device, the recording paper feed unit is disposed on the other side of the device on the lower portion thereof, and the upper portion of the recording paper feed unit is used as the region where the clamper is moved. With this arrangement, however, when the recording paper is to be fed by being held by the clamper, it is fed through a path starting from the recording paper feed unit, and arriving at the clamper by reversing the direction thereof by turning around the platen roller. As a result, there is a possibility that the recording paper is not fed well, because the paper is not smoothly moved around the platen roller due to the rigidity (stiffness) thereof. To cope with this problem, a guide must be provided to regulate the feed direction of the recording paper moving around the platen roller. Since, however, this guide means cannot be provided at a position interfering with the recording head when an image is formed, a problem arises when the recording paper is fed.
The platen roller is rotatably arranged and a pinch roller is pressed thereagainst. The recording paper is pressed against the platen roller by the pinch roller and can be fed to the position where the recording paper is held by the clamper, by the rotation of the platen roller. When, however, the platen roller is in a resting state, the pinch roller is continuously pressed against the same position of the outer periphery of the platen roller. As a result, a pressed recess may be defined in the elastic member forming the surface of the platen roller, by the pinch roller. When the pinch roller is removed from the platen roller, this recess gradually recovers and the surface of the platen roller returns to its original state. However, the recording paper is pressed against the recording head with an irregular press force in the peripheral direction of the platen roller (in the auxiliary-scanning direction) from the time when an image formation is started to the time when the recess disappears (when the recessed portion confronts the recording head, the press force is reduced). Thus, a problem arises in that a bad image formation is caused by the above recess.
Further, when an image formation is carried out a plurality of times in the color imaging device as described above, the recording paper must be returned to the image formation start position each time the image formation is carried out. At this time, the retracting speed of the clamper must be synchronized with the circumferential speed, in a reverse direction, of the platen roller with a pinpoint accuracy, so that the recording paper is not loosened, or a clamped position of the recording paper is not dislocated by an excessive tension applied thereto. Thus, a problem arises in that the arrangement and control of the imaging device are made complex. Note, when the recording paper is loosened, wrinkles are developed in the recording paper, and when the clamped position is dislocated, a bad image is formed on the recording paper due to the relative dislocation of colors.
A heat sensitive recording system is employed to form an image by using the recording head on a recording paper moved as described above. In this system, solid-melted inks or sublimated-pigment inks are supplied by being coated on a base film. When color materials are supplied by an ink ribbon, the recording paper being scanned and the ink ribbon placed thereon are moved together between the platen roller and the recording head disposed in close proximity to the platen roller. The image is formed by transferring the color materials onto the recording paper. In the imaging device arranged as described above, if the ink ribbon is not moved in perfect synchronism with the scanning/movement of the recording paper, a problem arises in that a resolution is lowered or colors are dislocated in the color imaging device. When, however, the ink ribbon is moved by being wound around a reel, the ink ribbon is moved at a different speed depending upon an amount of the ink ribbon wound (because the diameter of the winding side reel is changed as an amount of the ink ribbon wound therearound is changed). Thus, the movement of the ink ribbon cannot be perfectly synchronized with the movement of the recording paper, and thus the speed of the ink ribbon is very difficult to constantly control.
Further, the ink ribbon is consumable and a new ink ribbon must be supplied when it is consumed. Usually, the ink ribbon is supplied as an ink ribbon cassette accommodating a reel around which a predetermined amount of an ink ribbon is wound and a reel for winding the ink ribbon. Thus, when the ink ribbon is totally consumed, the entire ink ribbon cassette is to replace. In an imaging device provided with a recording head having recording elements disposed over the entire width of a recording paper and using the aforesaid ink ribbon, however, an ink ribbon as wide as the width of the recording paper to which an image can be formed must be moved between a platen roller and the recording head, together with the recording paper. Further, a new ink ribbon cassette must be easily installable.
An imaging device using usual papers cut to a predetermined size is arranged such that a recording paper cassette accommodating the recording papers (usual papers) is detachably mounted to the paper feed unit. The recording papers are fed from the recording paper cassette to the imaging device one by one so that an image can be formed thereon. With this arrangement, a size of the recording paper can be easily changed by replacing (switching) the recording paper cassette.
In the imaging device supplying the recording papers from the detachably mounted recording paper cassette, a feed device such as a feed roller, or the like, for introducing the recording papers accommodated in the recording paper cassette to the imaging device (i.e., supplying the recording papers from the recording paper cassette) is disposed on the imaging device side. Therefore, the recording papers accommodated in the recording paper cassette must be able to be fed while keeping a predetermined relative positional relationship with the feed means disposed on the imaging device side in the state that the recording paper cassette is mounted to a predetermined position of the imaging device. Thus, in a imaging device having the feed roller provided therewith, the recording papers must be pressed against the feed roller.
When, however, this arrangement is provided with the recording paper cassette, the recording paper cassette is made complex and a cost is increased.